Remove gcc_version from gyp and gn files.

build/config/gcc/gcc_version.gni

-# Copyright 2014 The Chromium Authors. All rights reserved.
-# Use of this source code is governed by a BSD-style license that can be
-# found in the LICENSE file.
-
-declare_args() {
-  # This allows the gcc_version to be overriden when using a custom toolchain.
-  # If the gcc_version is {X}.{Y}, set this value as XY.
-  gcc_version = -1
-}
-
-if (gcc_version == -1) {
-  if (is_android) {
-    gcc_version = 49
-  } else if (current_toolchain == "//build/toolchain/cros:target" ||
-             current_toolchain == "//build/toolchain/linux:mipsel") {
-    gcc_version = exec_script("../../compiler_version.py",
-                              [
-                                "target",
-                                "compiler",
-                              ],
-                              "value")
-  } else if (current_toolchain == "//build/toolchain/linux:x64" ||
-             current_toolchain == "//build/toolchain/linux:x86") {
-    # These are both the same and just use the default gcc on the system.
-    gcc_version = exec_script("../../compiler_version.py",
-                              [
-                                "host",
-                                "compiler",
-                              ],
-                              "value")
-  } else {
-    gcc_version = 0
-  }
-}